The present invention relates generally to the field of hardness testing, and in particular, to an apparatus and method for testing the hardness of battery components such as battery lugs.
A typical automotive battery generally includes a container which is separated into a plurality of compartments by a series of partitions, and a plurality of cell groups which are positioned within each of the compartments and appropriately interconnected to complete the assembled battery. Each cell group typically comprises a series of interleaved positive and negative plates; respective positive and negative plates being appropriately interconnected by straps extending therebetween. To assemble the finished battery, these straps must be appropriately interconnected so that the positive strap of one cell group is connected to the negative strap of an adjacent cell group. One way that this may be accomplished is by providing each of the partitions with an aperture, and by providing each of the battery straps with an upstanding lug positioned so that adjacent lug pairs can be connected to each other through the aperture of the partition using any of a variety of techniques. One technique which can be used for the purpose is resistance welding. Examples of this may be found, for example, in my U.S. Pat. No. 4,166,210, the subject matter of which is hereby incorporated by reference as if fully set forth herein.
Generally, the technique illustrated in U.S. Pat. No. 4,166,210 calls for flat outer surfaces of the battery lugs to be positioned adjacent the partition and substantially enclosing the aperture. Thereafter, a pair of weld jaws are positioned adjacent the exposed surfaces of the battery lugs so that electrodes attached to the weld jaws can extrude portions of the lug material into the aperture of the partition. Upon achieving proper contact, an electric current is directed through the weld jaws, the electrodes and the battery lugs. A strong and efficiently produced weld results, providing the desired intercell connection.
The foregoing technique has been found to work extremely well in providing strong and efficiently produced intercell welds. However, despite the improvements afforded by such a technique, it has been found that a significant number of batteries still must be rejected for failure to achieve a proper intercell weld. Since a typical automotive battery generally includes five such welds, the problem is multiplied, since the failure of any one of these welds can result in rejection of the battery. For this reason, continued attempts have been made to further refine this technique.
One variable which has been found to affect weld performance relates to the amount of pressure which must be applied to the battery lugs to achieve their proper contact whithin the aperture of the partition. Applying too much pressure can cause excessive contact between the battery lugs, while applying too little pressure can cause insufficient contact. In either case, an improper resistance is developed across the battery lugs, adversely affecting the resulting weld. However, by properly regulating the pressure applied to the battery lugs, substantially improved intercell welds can be produced.
One difficulty which has been encountered in satisfactorily regulating the pressures applied by the weld jaws relates to the non-uniformity in hardness of such battery lugs, particularly between different production lots. Clearly, variations in hardness can adversely affect the amount of lug contact produced when a given pressure is applied by the weld jaws. It is therefore desirable to obtain an accurate indication of the hardness of the battery lugs being used in a particular application before the operational parameters of the welding apparatus are set.
A variety of devices have been used in an attempt to obtain such a measurement. Perhaps the most sophisticated hardness tester used for this purpose is the Rockwell Model JS Hardness Tester, however, satisfactory results have still not generally been obtained. Rather, substantial variations have often been found to occur between measurements performed on lugs from different, or even the same production lots, and even between separate measurements performed at two different locations on a single lug. Moreover, a surprising lack of corrolation has been found to exist between the hardness value measured by the hardness tester and the actual performance of the intercell welding apparatus after being set to accommodate a battery lug having such a hardness value. Such variations have made it exceedingly difficult to accurately predict the amount of pressure which must be applied by the weld jaws to achieve a proper intercell weld.
It, therefore, remains desirable to develop an apparatus which can accurately and reliably determine the hardness of a battery lug, so that the intercell welding apparatus can be calibrated to achieve a proper intercell weld.